Currently, when you have a skill bound to mouse1, and that skill is on cooldown, your character will instead try to use their default attack instead.
This is good sometimes, but bad in other places. For example, there is a bone harvest spam build where bone harvest has a 0.2s cooldown, and some versions of stun jacks where stun jack has a 0.1s cooldown.
If you bind those buttons to mouse1, and hold down left-click, what will happen is your character will alternate between bone harvest and default attack, resulting in less bone harvests per second than if the button was keybound somewhere else.
It would be to let the player choose the behaviour of mouse1, otherwise some builds might be forced to use clunky keybinds (meaning for some players, some builds will be dead on arrival)
(i play WASD, i haven’t tried with click-to-move)